Hydrodynamic behaviour of mollusc shell debris: influence of faunal composition

• Main Authors: Rieux, Alissia, Weill, Pierre, Mouazé, Dominique, Tessier, Bernadette
• Other Authors: Morphodynamique Continentale et Côtière (M2C), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: Bioclastic sediment; Settling velocity; Carbonate sediment; Threshold of motion; Boundary layer; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Crassostrea gigas
• Online Access: https://hal-normandie-univ.archives-ouvertes.fr/hal-02166657

International audience Understanding the hydrodynamic behaviour of bioclastic particles is necessary to refine our interpretation of depositional environments in the fossil record and to improve predictive numerical models for coastal zone management. Many coastal sediments are partly composed of biogenic particles, which shapes and densities differ strongly from classic rounded quartz grains. This results in particular hydrodynamic behaviours. Characteristics of biogenic particles can also vary significantly between species. If numerous studies have investigated the hydrodynamic behaviour of bioclastic sediments derived from reef-dwelling organisms, there is a paucity of research focusing on “cool-water carbonate” bioclastic particles (i.e. mollusc shell debris, calcareous algae,.). The aim of the present research is to characterize the influence of faunal composition on the settling velocities and the entrainment threshold of mollusc shell debris from temperate regions. Shells have been sampled in the southern coast of Mont-Saint-Michel bay (Brittany, France) which is bordered by a coarse, shelly coastal barrier, before being ground and separated into individual sieve fractions. Eight species representative of the faunal composition in the area have been studied: four wild species (Cerastoderma edule, Scrobicularia plana, Anomia ephippium, Ostrea edulis) three reared species (Crassostrea gigas, Mutilussp., Ruditapes philippinarum) and one introduced (Crepidula fornicata). Settling velocities of the eight species have been measured in a settling tube for several debris sizes. A set of experiments have been performed in a small recirculating flume. Threshold of motion of the species under unidirectional current for different grain sizes have been characterized using an Acoustic Doppler Velocimeter Profiler. Critical bed shear stress values (tau_cr) were derived from velocity profiles in the boundary layer, by a logarithmic regression of the “law of the wall”.Results show consistent interspecific differences in ...